1. Technical Field
The present invention relates to an optical-modulation object, and more specifically, to an optical-modulation object in which birefringent island-in-the-sea yarns having two or more spinning cores are present in a matrix, to considerably reduce production costs and remarkably increase luminance.
2. Background Art
Optical-modulation objects comprise an inclusion dispersed in a continuous matrix, which are well-known in the art and are widely utilized in a variety of optical devices and liquid crystal displays, etc., requiring optical modulation. By modulating the characteristics of inclusions, a predetermined range of reflectivity and transmittance can be imparted to optical-modulation objects. These characteristics include the size of inclusions in an object relative to a wavelength, the shape and arrangement of inclusions, volume ratio of inclusions and mismatch levels in refractive index between an object and a matrix continuously arranged along three rectangular axes, etc.
Common absorptive polarizers comprise inorganic blocked chains containing light-absorbing iodine arranged in a polymer matrix as an inclusion thereof. Such a film absorbs light polarized according to its electric field vectors arranged parallel to blocked iodine chains and transmits light polarized perpendicular to the blocks. Since iodine chains have two or more dimensions smaller than wavelengths of visible rays and have a great number of chains per a cube of ray wavelength, the optical-modulation object has the same optical properties as a mirror surface (specular), and diffusive transmission through the optical-modulation object or diffusive reflection from the surface of the optical-modulation object is very slight. Like most other commercially obtainable optical-modulation objects (See FIG. 1), such an optical-modulation object is based on selective absorption and reflection of polarized light.
Optical-modulation objects filled with inorganic inclusions exhibiting different properties provide different optical transmittance and reflectivity. For example, mica flakes having two or more dimensions larger than wavelengths of visible rays are incorporated into a polymer film and a paint, to impart metallic luster thereto. By designing the flakes to be present in the plane of the film, strong direction-dependency can be imparted to reflection behaviors.
The use of these effects enables production of safe screens that have a high reflectivity at a specific observation angle and have a transmittance at other observance angles. Large flakes rendering color (selective regular reflection) depending on the arrangement state of incident light are incorporated into films, to provide evidence of reflection (tampering). For this purpose, flakes present inside the films should be uniformly arranged.
However, optical films produced from polymers filled with the inorganic inclusions have a variety of disadvantages. Commonly, the adhesion between inorganic particles and a polymeric matrix is bad. Accordingly, optical properties of optical-modulation objects are deteriorated, when stress or deformation is alternately applied to the matrix. This is because the bond between the matrix and the inclusion may be damaged and hard inorganic inclusions may be broken. Additionally, further considerations are required in the process for arranging inorganic inclusions, thus complicating a production process.
However, both a matrix and an inclusion inserted into the same, which constitute conventional optical-modulation objects, are optically isotropic, thus disadvantageously causing deterioration in optical modulation efficiency. When birefringent fibers are arranged in a matrix, light emitted from a light source is reflect, scattered and refracted on the birefringent interface between the birefringent fiber and the isotropic matrix, thus inducing optical modulation and improving luminance. However, general birefringent fibers have advantages of low production costs and high optical modulation efficiency, but disadvantageously cannot improve luminance to a desired level and are unsuitable for application to industrial fields, instead of conventional optical-modulation objects comprising inclusions.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an optical-modulation object comprising birefringent island-in-the-sea yarns designed to prevent aggregation of island portions and thus maximize optical modulation efficiency and a method for fabricating the same.